Right hundreds of knights charging straight into the arrows on the mud despite seeing consequences of such action again and again at crecy and poitiers isn't a debacle,especially when u outnumber enemy almost laughably.

Same when u lose 60000 men in one day,thats a debacle.hundreds of soldiers running straight into machine guns and cannons.
British aura of confidence and self belief built up over a 100 years of pax britannia was smashed totally in a single day.They didn't recover their self confidence to that degree till battle of britain.
Fear of Battles like somme were one of the main reasons behind appeasement policy.

Great Britain was really rather good at loosing battles in the 1OO years prior to the Somme. The Zulus and The Boer and the Mhadi all had their moments.

Great Britain was really rather good at loosing battles in the 1OO years prior to the Somme. The Zulus and The Boer and the Mhadi all had their moments.

The Zulus won one battle against a camp guard force, something of a Pyrrhic victory, but all the same a battle the British guard force should have won
Even so, the Zulus were a magnificently disciplined force - yet 100 soldiers held off 4,000 Zulus the same day

The Boers won several battles early in the 2nd Boer War, but nothing like total annihilation

The Mahdi was one man, not a people and AFAIK, he never beat a British field army. His forces did kill a British general at a siege of a Sudanese city and a British colonel commanding an Egyptian field force

In 1939, no-one rushed to don khaki...they waited for their call up papers.

Yes London witnessed scenes of jubiliation when war broke out, but comparable scenes were being played out in Vienna,Paris,Berlin and even St Petersburg. Dont forget it was supposed to be a short war, `Bash the Hun and home for Xmas`. There was also a strange and I hope never to be repeated sentiment at the time that we `needed a war, it would somehow cleanse Europe of its ills`

In 1939, no-one rushed to don khaki...they waited for their call up papers.

I think that totally distorts the situation. The mass "flocking to the colours" didn't occur until after the retreat from Mons and Kitchener's call to arms. Even during WW1 it was realised that the whole building of the "New Army" had been a debacle. There had been no equipment, no uniforms, no barracks accomodation, insufficient NCOs for training and so on. Worse, no account was made of skills and recruits were allocated just anywhere, ensuring that 40 year old factory manager might just be in the same trench as the 18 year old schoolboy. The territorials and militia before WW1 had really been little more than drinking clubs and totally unsuited for early combat.
Before WW2, especially after the Munich crisis the structures were put in place to rapidly expand the armed forces in a logical manner with registration for conscription, although not its implementation, expansion of the reserves and wide-ranging exemptions for people in key occupations. On the outbreak of war the government specifically requested people NOT to flock to recruiting stations and "wait their turn", although this didn't deter them. A big point of contention was those in "reserved occupations" who were not permitted to join the armed forces initially. In 1939 most of those called up were people who had joined the reserves before the outbreak of war.
The situation changed in 1940 after the fall of France when both the Army got its act in gear to speed up the process of recruitment and in proving that volunteering was not dead, a radio broadcast by Anthony Eden for volunteers for the Home Guard (Local Defence Volunteers) saw 250,000 overage, underage and occupationally disqualified men volunteer within seven days and a further 1.5 million within two months. That is more than the 700,000 who volunteered for Kitchener's Army in 1914 and a respectable number against the total volunteer strength of WW1 of 2.5 million.